UV unwrapping doesn't use full UV Space, but roughly a quarter of it
Blender generally scales the UV relative to the longest (fully self-connected) piece. To make it take the full space, add seams to the longest piece(s), to make it roughly the same &quot;size&quot; as the rest of the islands:
(Note - the places I have marked for seams are only general suggestions of where to put them - you will have to find and mark the edges that make the most sense for your object - just try to keep the islands roughly the same size as your other group of islands)